untilparameters always refer to sent emails, regardless of which metric was requested. Metrics are retrieved from emails which were sent within the date range defined.
For example, if you're requesting data on reviews within the date range of Jan 01 (
since) - Jan 05 (
until), note that while the review request emails were sent within the date range, the actual reviews may have only been created after Jan 05 (
date_bucketdefault value is
monthand returns values as a calendar month:
For example, &since=2017-07-15&until=2017-08-15&date_bucket=month will return monthly buckets as July 15 -31, August 01 - 15